1. varNum is defined on frame 1 of mc2
2. mc2 is on frame 1 of mc1
3 mc1 is on frame 1 of the _root timeline
4. you try and access varNum (with the correct path) in frame
1 of the _root timeline and fail because the code in frame 1 of the
_root timeline executes before the code in frame 1 of mc2. so,
varNum appears to be undefined.

Thanks Kglad,
The issue I was having with the example I had created was
indeed as you pointed out to do with timing.... however, for my
actual problem I was getting the variable value using an onRelease,
so wasn't a timing issue, but infact an incorrectly spelt instnace
name... school boy error... far too tired. Sorry for wasting your
time, and thanks for the response.
J